The present invention relates to a device for transporting particles of a magnetic material in a selected direction. There are various fields of technology in which it is desired to transport particles of a magnetic material, for example continuous separation of paramagnetic particles from a stream of fluid or continuous grid cleaning operations. In the description hereinafter, particles of a magnetic material are understood to be particles which are attracted by a magnet which induces a magnetic field extending into the area where the particles are present.
Accordingly it is an object of the invention to provide a device for transporting particles of a magnetic material in a selected direction.
The device according to the invention comprises:
a support member having a support surface for supporting the particles, the support surface extending in the selected direction;
a magnet arranged to generate a magnetic field retaining the magnetic particles on the support surface, the magnetic field having at least one region of reduced field strength at the support surface relative to a field strength of the magnetic field at the support surface outside said region; and
drive means for moving each region of reduced field strength relative to the support surface in a direction having a component in the selected direction.
It is thereby achieved that, when particles of a magnetic material are supplied to the support surface, the magnetic forces exerted to the particles are lower at the region of reduced field strength than outside said region. Thus, the particles tend to adhere stronger to the surface outside said region than in said region, and by moving the region of reduced field strength relative to the support surface, the particles tend to follow such movement. The magnetic material can be, for example, a material having ferromagnetic, ferrimagnetic or paramagnetic properties.
In an attractive embodiment of the invention said particles are abrasive particles and the device forms part of a tool for excavating an object, the tool including a jetting system having a mixing chamber provided with a first inlet for a fluid, a second inlet for abrasive particles and an outlet nozzle arranged to jet a stream of fluid and abrasive particles against the object during excavating the object with the tool, and wherein the device is arranged so that the support surface is exposed to said stream downstream impingement of the stream against the object and that the particles are transported by the device towards said second inlet.
Suitably the tool forms a drilling tool for drilling a borehole in an earth formation, and wherein the object forms the wall or the bottom of the borehole.
Alternatively the tool forms a milling tool for milling an opening in a wellbore tubular, and wherein the object forms the wall of the wellbore tubular.
It is preferred that the stream flows along the device (downstream impingement against the object) through a conduit of non-magnetic material.